In the turbine section of a gas turbine engine turbine discs rotate next to fixed stator structure. In order to prevent turbine gases leaking from the gas turbine annulus inwards onto the disc faces a seal structure is arranged between the rotor and stator.
The seal structure is provided with a radial clearance which provides a tortuous path for the turbine gases. To reduce the gas leakage through the seal the clearance of the seal is set to a minimum during stabilised engine running. However during transient conditions, such as an engine acceleration, differential radial growth occurs between the rotor and stator and the seal clearance is reduced. Radial incursions cause seal rub and abrasion which increases the seal clearance. The increased seal clearance allows leakage through the seal when the engine returns to the stabilised running condition.